The present invention relates generally to image forming equipment and is particularly directed to an intermediate transfer member (ITM) module of the type which limits the lateral movement of the ITM belt. The invention is specifically disclosed as an ITM module that passively limits lateral belt movement by controlling dimensional characteristics of certain components, and by providing angled tracking guides to further limit such lateral belt movement.
When a belt is driven around a system of rollers in an electrophotographic (EP) printer, such as a laser printer, a lateral motion (i.e., in the scan direction) can occur in addition to the motion in the driven direction (i.e., in the process direction). Without intervention, it is likely that the belt will continue to move laterally, ultimately running off the ends of these rollers, thereby damaging the belt and ending the life of the belt module.
Conventional belt transport systems that control lateral belt motion by use of contoured rollers (crowned, saddled, etc.) are unable to be used on many EP printer belt systems. Contoured rollers can only be used with relatively elastic belts that are not damaged when forced to conform to a roller having a shape that is not purely cylindrical. (If the belt does not conform to the roller, the lateral motion is poorly controlled.) Due to the material properties of some belt modules in many EP printers, which typically are both stiff and fragile, contoured rollers cannot be used. Also, when used as a means to transport media or toner, contoured rollers can induce misregistration and transfer problems across the width of the image.
A number of current ITM belt modules use tracking systems that attach items directly to the belt, such as edge reinforcements (e.g., tape), and/or guiding geometry materials (e.g., elongated beads of material) which are used in conjunction with flanges and/or steps in the rollers to control the lateral motion of the belt. These xe2x80x9cattachmentsxe2x80x9d have typically comprised tape, and/or guiding strips, ridges, or xe2x80x9cbeadsxe2x80x9d of material (e.g., elongated beads of epoxy or another fluidic dispensable material, or strips of solid material) that are applied to the belt, usually on the inside of the belt in an EP printer. The belt is then allowed to move laterally against a flange or a stop. In one example, the tape allows the flange to exert enough force to counteract the lateral motion of the belt without damaging the belt edge. In another example, a thick xe2x80x9cbeadxe2x80x9d of material is attached to the belt. The rollers then have appropriate steps or grooves to accommodate the bead. When the belt moves laterally, the bead comes into contact with the edge of the step/groove, which restricts the lateral motion.
The conventional methods described above have a number of drawbacks, as follows:
(1) Tape, beads, or any items attached directly to the belt are additional operations in the belt manufacturing process and so add cost and complexity to the belt.
(2) Many EP printer belt materials have surface properties that prevent adequate adhesion. It is then problematic and/or costly to obtain a belt, adhesive, and tape and/or bead combination which will last a sufficiently large number of revolutions, say 100,000 or more, without losing the bond and then damaging the system. Many material combinations will only last 30,000 to 60,000 revolutions. This is worsened when belt systems must be made smaller to limit the footprint of an EP printer. Such smaller modules incorporate one or more small diameter rollers, typically less than 18-20 mm in diameter, and/or reverse rollers that expose the belt to bidirectional bending. Small diameter rollers and reverse bending create more stress from flexure which then causes tape and/or beads to crack and peel from the belt, thereby limiting belt life to as few as 25,000 to 45,000 revolutions.
(3) If the lateral position of the belt is set by the belt""s edge (e.g., with reinforcing tape and flanges), even small amounts of unevenness in the belt edge and tape edge location (e.g., 0.2 mm to 0.4 mm) can cause irregular lateral motion of the belt. This can cause skew disturbances in the registration between colors in single-pass color EP systems. This is also true of beads. The unavoidable lack of straightness or variations in the thickness and/or lateral location of the bead edge by, for example 0.2 mm to 0.4 mm, can cause skew or registration problems.
(4) Items applied to the belt can generate problems in cleaning residual toner or other development materials from the belt when using a blade cleaner. Tape creates an effective step change in thickness. The step can be minimized by cutting a step of the width and thickness of the tape into the rollers and any other belt supports. However, due to tolerances, the step in the roller/support and the width and thickness of the tape or bead on the belt rarely have the exact canceling effect necessary to create a truly smooth supporting surface underneath the belt as it passes under a cleaner blade, and a gap or step will still occur. Any step change in the supporting surface of the belt creates cleaning problems for a blade cleaner. For wide belt modules, this can be solved by only printing and cleaning on the area of the belt that is within the tape. However, this can significantly increase the width of the belt module and of the EP machine, and leaves the potential for toner contamination. When belt modules must decrease in size to allow an overall decrease in the EP printer size, the blade cleaner is forced to operate over the top of any tape or beads. With such a configuration, the use of tape or beads typically causes early cleaning failure, i.e., at 30,000 to 60,000 prints, rather than a more desirable 100,000 or more prints.
Yet another method of controlling lateral belt motion is through the use of active steering. This requires costly sensing and activation means, that is, one or more sensors and at least one actuator (e.g., an additional motor with control circuitry, or a mechanism actuated by belt position), as well as a large lateral movement range to initially determine the motion of the belt and to begin controlling the belt. Such systems can be implemented using mechanical, electrical, pneumatic, or other means. The capture range significantly increases the width of the machine, thereby driving up the cost and machine footprint.
In view of the problems associated with conventional belt systems in EP printers, it would be an improvement to provide a belt module for an EP printer that utilized a passive tracking technique without the use of attachments (i.e., tape or xe2x80x9cbeadsxe2x80x9d) to the belt itself, while at the same time preventing the belt from excess lateral motion. Such a system could utilize a reliable low cost method to control the lateral motion of the belt, without use of edge reinforcements, or other auxiliary parts or treatments applied to the belt.
Accordingly, it is an advantage of the present invention to provide an ITM belt system that minimizes the lateral tendency of the belt by tightly controlling the roll alignment/parallelism.
It is another advantage of the present invention to provide an ITM belt system that minimizes the lateral tendency of the belt by minimizing the walk rate through use of an adjustment roll.
It is yet another advantage of the present invention to provide an ITM belt system having a characteristic of making the belt tracking position relatively insensitive to variations in the torque required to drive the belt system.
It is still another advantage of the present invention to provide an ITM belt system having the ability to control the lateral position of the belt without edge reinforcement and without the use of external actuators, which further allows residual toner to be effectively cleaned from the entire belt width, thereby allowing a smaller width for both the belt system and its EP machine.
It is a further advantage of the present invention to provide an ITM belt system having the ability to form a stable lateral belt position, through use of the angled tracking guides located near one of the rolls.
It is yet a further advantage of the present invention to provide an ITM belt system having the ability to form a stable lateral belt position, without the use of moving parts to control belt positioning.
Additional advantages and other novel features of the invention will be set forth in part in the description that follows and in part will become apparent to those skilled in the art upon examination of the following or may be learned with the practice of the invention.
To achieve the foregoing and other advantages, and in accordance with one aspect of the present invention, a belt system having a passive lateral tracking system is provided, in which the system comprises: a continuous belt member which travels along a predetermined pathway that is formed by a plurality of rolls; at least one tracking guide that is positioned a predetermined distance from one of the plurality of rolls, wherein the at least one tracking guide tends to limit a lateral movement of the belt member as the belt travels along its predetermined pathway.
In accordance with another aspect of the present invention, a belt system having a passive lateral tracking system is provided, in which the system comprises: a continuous belt member which travels along a predetermined pathway that is formed by a plurality of rolls; and wherein at least two of the plurality of rolls are positioned such that their parallelism is held to a predetermined substantially small angular value, to minimize an effect of external forces on belt walk rate in a lateral direction.
In accordance with a further aspect of the present invention, a belt system having a passive lateral tracking system is provided, in which the system comprises: a continuous belt member which travels along a predetermined pathway that is formed by a plurality of rolls; and wherein at least one of said plurality of rolls exhibits a roll conicity/flare of a predetermined maximum diametral variation within a roll, along the entire width of the roll.
In accordance with still another aspect of the present invention, a belt system having a passive lateral tracking system is provided, in which the system comprises: a continuous belt member which travels along a predetermined pathway that is formed by a plurality of rolls; and wherein a position of one of the plurality of rolls is adjusted along a predetermined line so as to minimize the belt walk rate.
In accordance with yet a further aspect of the present invention, a method for controlling lateral movement of a belt member in a belt system is provided, in which the method comprises the steps of: (1) providing a belt system having a continuous belt member which travels along a predetermined pathway that is formed by a plurality of rolls; (2) controlling dimension tolerances of predetermined components of the system; (3) adjusting a position of a first of the plurality of rolls with respect to a second of the plurality of rolls, thereby tending to minimize a walk rate of the belt member as the belt member travels along its predetermined pathway; and (4) providing at least one tracking guide that is positioned a predetermined distance from one of the plurality of rolls, wherein the at least one tracking guide tends to limit the lateral movement of the belt member as the belt member travels along its predetermined pathway.